1. Field of the Invention
The present invention relates to a linear actuator and more particularly, to the structural design of the housing of a linear actuator, which is formed of two half shells, facilitating installation and position adjustment of limit switches.
2. Description of the Related Art
Many linear actuators are known and intensively used in electric hospital beds, treadmills and to facilitate position adjustment. During application of a linear actuator, limit switches are usually used and respectively mounted in the start end and finish end to control the forward and return strokes of the linear actuator. When a push block of a nut of the linear actuator touches the limit switch at the finish end during the forward stroke, the limit switch is triggered to stop forward movement of the linear actuator. On the contrary, when the push block of the nut touches the limit switch at the start end during the return stroke, the limit switch is triggered to stop backward movement of the linear actuator. Thus, the linear actuator is controlled to reciprocate with the start end and the finish end.
FIG. 7 is an exploded view of a linear actuator according to the prior art. According to this design, the linear actuator comprises a housing A, a driving mechanism B, and two limit switches C. The housing A comprises a hollow base A1, and an outer tube A2 that extends from one side of the hollow base A1 and defines therein a longitudinal receiving chamber A21. The driving mechanism B comprises a motor B1 fastened to one side of the hollow base A1 of the housing A, a worm B11 fixedly connected to the output shaft of the motor B1 and inserted into the inside of the hollow base A1 of the housing A, a spindle B2 rotatable mounted in the longitudinal receiving chamber A21 of the outer tube A2 of the housing A, a worm gear B21 fixedly mounted on one end of the spindle B2 and meshed with the worm B11, a nut B3 threaded onto the spindle B2 and supported inside the longitudinal receiving chamber A21 of the outer tube A2 of the housing A and movable linearly relative to the spindle B2 during rotation of the spindle—B2, and a push rod 4 threaded onto the spindle B2 and extending out of the outer tube A2 of the housing A for connection to an external driven member. The nut B3 has a push block B31 protruded from the periphery thereof. Further, a rail C1 is mounted in a longitudinal groove A22 inside the longitudinal receiving chamber A21 of the outer tube A2. Further, two limit switches C are mounted on the rail C1 at selected locations at two opposite sides relative to the push block B31 of the nut B3 at the spindle B2.
When started the motor B1, the worm B11 is driven to rotate the worm gear B21 and the spindle B2, causing forward or backward movement of the nut B3 and the transmission shaft B4 relative to the spindle B2. When the nut B3 reaches a predetermined position, it will touch one limit switch C, causing the limit switch C to stop the motor B1. In actual practice, this design of linear actuator still has drawbacks as described hereinafter.
During installation of the linear actuator, the rail C1 and the limit switches C are mounted in the longitudinal groove A22 inside the longitudinal receiving chamber A21 of the outer tube A2 of the housing A subject to the use of a scale, and then the spindle—B2 and the nut B3 are inserted from one end of the longitudinal receiving chamber A21 into the inside of the outer tube A2 of the housing A, and then the transmission shaft B4 is inserted from the other end of the longitudinal receiving chamber A21 into the inside of the outer tube A2 of the housing A and threaded onto the spindle—B2. During insertion of the spindle B2 and the nut B3 into the longitudinal receiving chamber A21 of the outer tube A2 of the housing A, the limit switches C may be biased accidentally by the push block B31 of the nut B3. When this problem happens, the user needs to re-install the rail C1 and the limit switches C. Further, when wishing to adjust the positions of the limit switches C, the user needs to detach all the parts of the linear actuator, solder the limit switches on the other position and rearrange the wires accordingly.
Therefore, it is desirable to provide a linear actuator that eliminates the aforesaid drawbacks.